Prostate cancer is the second leading cause of all cancer-related deaths and the most commonly diagnosed cancer among males in US. Castration-resistant prostate cancer (CRPC) is an incurable and lethal form of the disease. Docetaxel-based chemotherapy is the first-line standard treatment for CRPC. However, the efficacy of systemic chemotherapy is limited by poor efficiency in the delivery, drug resistance and systemic toxicity. The goal of this project is to develop novel stimuli-responsive cross-linked theranostics (SCTs) for image-guided delivery of mechanism-based molecular medicine to circumvent treatment-resistance and systemic toxicity for advanced prostate cancer. SCTs integrate unique stimuli-responsive crosslinking strategies and highly potent av3 integrin targeting ligand (LXW64) into a novel multifunctional nanoporphyrin system with unique architecture-dependent imaging properties. The goal of Aim 1 is to design and synthesize a series of SCTs with boronate, disulfide and protease-cleavable crosslinkers that are responsive to the intrinsic stimuli at the tumor microenvironment, such as acidic pH, reducing agents and proteases, respectively. SCTs will be decorated with LXW64 to enhance their targeting capability to advanced prostate cancer. In Aim 2, the spatiotemporal distribution of SCTs including pharmacokinetics, biodistribution and intratumoral delivery and drug release, will be quantitatively investigated by multimodal imaging (NIRFI, PET and MRI) in orthotopic prostate cancer xenograft models. The 64Cu signal of SCTs from PET imaging will be measured quantitatively so that the pharmacokinetics and biodistribution of SCTs can be determined. The activation of the MRI and NIRF imaging functions correlates with the level of local stimuli and can be considered as an indication of nanoparticle dissociation and drug release. The imaging results will be validated by inductively coupled plasma mass spectrometry (ICP-MS) for quantitative Gd level, autoradiography and frster resonance energy transfer (FRET) for drug release as well as immunohistochemistry for protease and integrin level. In Aim 3, SCID mice bearing docetaxel-resistance prostate cancer xenograft will be treated with SCTs that are co-loaded with a new heat shock protein 90 inhibitor (ganetespib) and docetaxel. These novel nano-formulations hold promise for circumventing drug efflux through P-glycoprotein and inhibiting alternative growth pathways, two important mechanisms of resistance to docetaxel. Tumor regression associated with response to therapy will be quantified by molecular imaging, and correlated with molecular changes in tumor microenvironment. Successful development of the proposed theranostic agents will significantly improve the imaging sensitivity for monitoring the therapeutic delivery process, and enhance the delivery of mechanism-based drugs to overcome docetaxel resistance. Results from this study will be significant not only in advancing the development of a novel theranostic nano-platform for effective therapy of advanced prostate cancer, but also in providing a new framework of using stimuli-responsive cross-linked theranostics for image-guided drug delivery.